. The applicant claims to have developed a carbohydrate tagging method to perform low resolution mapping to locate the surface residues of TNF alpha trimer responsible for binding to the 55 kd receptor as the base of the TNF alpha timer and a pocket structure formed between neighboring monomers. This proposal will extend this carbohydrate tagging study into locating the surface regions on TNF alpha trimer responsible for binding to the 80 kd receptor. High resolution mapping employing alanine scanning mutagenesis will then be performed to determine the exact residues and the nature of their side chains in interacting with either the 55 kd receptor or 80 kd receptor. The role of the trimeric structure of TNF alpha in effecting receptor binding will be examined by the generation of heterotrimers containing monomers bearing different alanine substitution mutations. This will yield knowledge on the spatial requirement of the various receptor binding residues for their abilities to effect receptor binding and bioactivities. These informations will be utilized to construct additional site specific mutants for TNF alpha and examine for their abilities to function as agonists and antagonists for TNF alpha. The effects of these TNF alpha agonists and antagonists on HIV infection will be examined in productive as well as in chronic infections.